A thermosensitive recording medium is obtained by grinding a colorless or pale colored basic leuco dye (henceforth referred to as “dye”) and an electron accepting color developing agent (henceforth referred to as “color developing agent”) each into fine particles, preparing dispersions, blending the dispersions, preparing a coating solution by adding a binder, a filler, a sensitivity improving agent, a lubricant and other aids and applying the coating solution on a support material such as paper, synthetic paper, film, plastic and the like. The color is developed instantaneously through a chemical reaction when heated using a thermal head, hot stamp, thermal pen, laser beam and the like to yield a recorded image. The thermosensitive recording medium is used extensively in facsimiles, terminal printers of computers, automatic ticket vending machines, measurement recorders and the like. Furthermore, the thermosensitive recording medium is also used to prepare documents such as various tickets, receipts, labels, bank ATM receipts, gas and electric meter print outs, transportation tickets and the like.
However, the dye and color developing agent present in a thermosensitive recording layer readily dissolve in various solvents, and preservation problems such as color development in blank paper, a decline in developed color intensity and the like are encountered when a plasticizer such as those present in inks (water and oil based inks), adhesives and the like comes in contact with a thermosensitive recording medium. In addition, papers for shipping slips, bills, receipts and the like need to be stamped, and stamp reception becomes a required quality as well as preservation.
For these reasons, thermosensitive recording media (References 1 and 2) wherein a protective layer containing inorganic pigments and porous starch particles has been installed on the thermosensitive recording layer have been used.
In addition, some thermosensitive recording media with protective layers containing aqueous starch solutions that had been gelatinized by heating and those with easily soluble modified starches have been proposed (References 3 and 4).    Reference 1: Japanese Patent Application Public Disclosure No. 2000-289333    Reference 2: Japanese Patent Application Public Disclosure No. 2000-177243    Reference 3: Japanese Patent No. 3324872    Reference 4: Japanese Patent Application Public Disclosure No. H09-263047